1. Field of the Invention
The present invention relates to a dental root canal instrument according to the preamble of claim 1 and to a production method for a root canal instrument.
2. Related Art
The present invention relates to a dental root canal instrument according to the preamble of claim 1 and to a production method for a root canal instrument.
Such root canal instruments of a first type are known in practice as xe2x80x9creamersxe2x80x9d or files. The working part of the generic root canal instruments is e.g. formed from a uniformly twisted rod having a triangular or tetragonal cross-section so that a cross section laid through the working part has three or four cutting edges distributed around the circumference of the instrument, the cutting edges extending up to the tip of the instrument.
Such generic instruments are used for cleaning infected root canals and to abrade material in the tooth root as evenly as possible around the circumference of the root canal. Since the portions of the tooth root adjacent to the root canal may be infected, it is desired that tooth material is removed, if possible, everywhere around the original free cross-section of the root canal.
Due to their inherent stiffness said generic root canal instruments remove not only more material on the outside of the bend of the root canal, but also have the drawback that in said area they exclusively treat the outer portion whereas there is no abrasion on the curve inside of said curved root canal area, so that foci of infection might be left there.
Said generic root canal instruments have cutting edge angles of less than 45xc2x0, i.e. the polygonal cross-sections are twisted such that the angle of the cutting edge relative to longitudinal axis of the root canal instrument is less than 45xc2x0. This results in an operation in which material is substantially removed in the root canal by rotating the instrument, with the instrument being advanced at the same time.
Generic root canal instruments of a second type are known as so-called xe2x80x9cHedstrxc3x6m filesxe2x80x9d. The working part of said files has a single coiled cutting edge so that only a single cutting edge can be seen on each cross-section laid through the working part. The cutting edge angle is here more than 45xc2x0 and ranges from 45xc2x0 to 90xc2x0. Consequently, this instrument entails an operation in which the instrument is moved back and forth in its longitudinal direction, as is known from the handling of files used in the wood- or metal-working industry.
With such an operation these root canal instruments of the second type do also not abrade material on the curved inside of the bent portion of the root canal and have the additional drawback that in comparison with the outer cross-sectional contour of the working area the inner core has a much smaller cross-section so that these instruments break easily when they are operated in rotating fashion in a way similar to that of the first-mentioned type of instrument.
DE 38 05 580 A1 discloses a tooth root-treating instrument whose tip is rounded to have a semispherical shape. As a consequence, there is no guide section. Furthermore, the two cutting edges extend into the tip portion.
U.S. Pat. No. 4,332,561 relates to a root canal instrument which comprises a semispherical tip which is followed by a small-diameter cylindrical attachment. Hence, the document does not show a guide section with only one cutting edge.
A further root canal instrument is already known from U.S. Pat. No. 5,464,362. The tip of said instrument is made conical like in the case of a drill; the tool comprises two cutting edges.
It is an object of the present invention to improve a generic root canal instrument such that it allows an operation that is as efficient as possible, i.e. a material removal that is an efficient as possible at the desired places of the root canal, and provides protection that is as high as possible against unintended material removal.
Furthermore, it is another object of the present invention to provide a method used for producing the root canal instrument of the invention, which while being very precise can be carried out easily and at low costs.
According to the invention a root canal instrument includes a working part which comprises three different portions: Firstly, the cap-like rounded and thus cutting edge-free tip of the working part (1st section), then the guide section (2nd section) which comprises a single cutting edge, namely exclusively over not more than 180xc2x0 of its circumference, so that this cutting edge arrangement can achieve a very selective or targeted effect on the removing action with the root canal instrument and thus a very selective treatment of the canal wall on the inside of bends, and finally the section (3rd section) making up the largest part of the working part, in which the working part comprises two or more cutting edges and permits a correspondingly efficient action of removal. Since the cutting edges are designed to extend in helical fashion, a large machined space is created for receiving the removed material, whereby the efficiently of the root canal instrument is enhanced.
Since said third section of the working part accounts for the largest length of the working part, it can be said that the working part is xe2x80x9cin principlexe2x80x9d equipped with two or more cutting edges, but in contrast to said principle the guide section and the tip of the working part may be equipped, as already described, with only one cutting edge (in the guide section) or without any cutting edge (on the tip). Depending on the diameter of the working part, the guide section may have a very small length, i.e. in the case of small ISO sizes a length of about 1 mm. Nevertheless, the cutting edge arrangement on the guide section permitsxe2x80x94even in the case of small lengths of said sectionxe2x80x94the desired guide action which makes it possible to exactly control a material removal on the inner wall of the curved portion of a root canal.
There may be provided an arrangement that is irregularly distributed around the circumference of the working part and comprises two or more cutting edges as a rule: For instance, cutting edges which are in relatively close vicinity with one another may have arranged diametrically opposite thereto a portion of the circumference of the working part without any cutting edge. The root canal instrument can rest with said cutting edge-free circumferential portion on a large area of the wall of the root canal and have a supporting effect which permits a particularly efficient removal work of the circumferentially opposite cutting edges on the wall of the root canal. Apart from this increased efficiency, such an arrangement of the cutting edges permits a reliable control of the material removal when material is just to be removed on a specific circumferential portion of the root canal.
When only two cutting edges are provided in principle, this will first of all result in a higher contact pressure for the two cutting edges, by comparison with the arrangement of several cuffing edges, and thus in an enhanced work performance and, secondly, depending on the design of the cross-sectional profile of the working part, in a very large machined space for receiving and possibly transporting away the removed material, whereby the efficiency of the cutting edges is further enhanced.
The arrangement of basically three cutting edges that are equally spaced apart from one another on the circumference of the working part may be chosen to achieve a practical and acceptable compromise when different, partly contradictory demands are to be met:
Firstly, the number of the cutting edges is sufficiently small for a high contact pressure of the cutting edges and thus for a high efficiency of the root canal instrument, secondly, the machined space is sufficiently large for transporting away the removed material, thereby enhancing the great efficiency of the root canal instrument, thirdly, the cross-sectional contour of the working part may be designed to be relatively sturdy, which increases the service life of the root channel instrument and its resistance to breakage, and thus reduces the risk of injury for the patient, and, fourthly, this arrangement permits an inexpensive production method for the working part in that said part can be made from a twisted rod material with a triangular or tetragonal cross-section.
The invention shall now be explained with reference to an embodiment regarding both the root canal instrument and the method, which embodiment is to be taken in conjunction with the drawings, in which: